Honestly, it's a tiny bathroom and you don't need much. I'd get a shower curtain you love, a cozy rug and towels you love to coordinate, and perhaps a soap pump/tissue holder/garbage can set that is nice. If you want to be daring, which I think is fine, a small bathroom like this is a great space for cool wallpaper you would not want to use elsewhere. Personally, for small powder rooms like this, my favorite look has always been a nice white matelasse shower curatin (first photo below), with crisp white towels. Horchow will monogram them and you can get good deals during their white sale, and I love having the monogram coordinate with the paint on the walls. The color you have is nice, or another lovely color option is Ben Moore Revere Pewter (see last photo below for one bathroom in this colorway), which really makes white towels pop, and would go great with the gray marbling in your floors. (Horchow has a good monogram thread to coordinate, too.) A nice white accessory set something like those would set it off nicely. Alternatively, the green is lovely, and would look nice with either mother of pearl or seaglass type accessories. I'd upgrade the shower curtain to something more luxe, for sure.

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Also, I forgot to add that upgrading to a more stylish mirror will work wonders. Uttermost is a brand I find to be pretty affordable on Wayfair, Overstock, Amazon, etc., with a lot of fun options depending on your style!